A conventionally known engine is provided with an EGR device that refluxes part of exhaust gas into intake air. Combustion temperature is reduced by the EGR device refluxing the exhaust gas (EGR gas), which contains a low concentration of oxygen, into the intake air, thereby reducing generation of nitrogen oxide. In such an engine, when the exhaust gas is refluxed for a long time in an idling operation state in which the exhaust gas contains unburned fuel, this unburned fuel adheres to the EGR device, potentially causing trouble to the EGR system. Some known engines perform such a control that, in the idling operation state, an EGR valve (exhaust gas reflux valve) is closed to stop the refluxing of the exhaust gas, as disclosed in Patent Document 1, for example.
The EGR device disclosed in Patent Document 1 opens and closes the EGR valve based on a detection signal from a clutch sensor configured to detect whether a clutch is on or off. Specifically, when a signal indicating that the clutch is off is acquired from the clutch sensor, in other words, when an acceleration operation is not performed, the EGR device determines that the engine is in the idling operation state, and performs control to close the EGR valve. However, for example, a power generator or a work machine is capable of operating while an accelerator is held at a certain position. Thus, when the accelerator is operated and held at a certain position under an operation condition that the exhaust gas contains unburned fuel, the exhaust gas is potentially continuously supplied to the EGR device.